Last night, both cats were hanging out by the open door / screen door, when I heard fighting. I don't know whether Boo did anything first, but Charybdis was attacking Boo when I got there, and they were both being very loud.

Boo has been more affectionate with me lately than he used to be. I wonder if she is jealous.

I got the squirt bottle and chased them into the bedroom, but squirting her wasn't slowing her down much, so I wound up throwing the bottle at her. I broke the bottle, and finally squeezed water all over her with it. Boo ran off, and I shut her in the bedroom for a bit.

I later herded her into the bathroom and went to bed. The kitty door in the bathroom door was locked, but she got out anyway by morning. She seemed fine again until Boo tried to walk past. She ran after him, knocking over my laptop. I threw something between them to break it up, then chased her and threw clothing over her, finally getting her back into the bedroom.

I taped over the cat door... maybe it'll work for now, and I got her back into the bathroom.

Is it possible that a strange cat could have been audible outside or nearby? That's usually what sets off spontaneous fighting like that -- cat A hears an unfamiliar cat, gets scared, and then sees familiar cat B and attacks in confusion. Cat B fights back (naturally), and then they're all upset with each other.

Unfortunately, I've forgotten what you're supposed to do to settle them down. Keep them separated for a while, and then gradual reintroduction, as if they were new cats, I think.